1. Field of the Invention
The present invention relates to a disc recording and/or reproducing apparatus equipped with a radio receiving function. More particularly, the present invention relates to a disc recording and/or reproducing apparatus having device for reducing electromagnetic interference in such the apparatus.
2. Background of the Invention
There are widely used composite audio apparatus such as radio-equipped cassette tape recorders each consisting of a combination of an AM-FM radio receiver and a stereo tape recorder employing a cassette tape as a recording medium, due to the convenient capability of recording radio broadcast programs with facility.
Of late, there is proposed a portable digital audio disc recording and/or reproducing apparatus which employs a rewritable optical disc such as a magneto-optical disc. A novel composite audio apparatus is currently contrived, similarly to the conventional radio-equipped cassette tape recorder, by combining such a digital audio disc recording and/or reproducing apparatus with a radio receiver.
In recording a data signal on a rewritable magneto-optical disc, a recording current corresponding to the data signal is supplied to a magnetic head while a light beam is irradiated to a recording layer on the disc to heat the same. As a result, new data is written simultaneously with erasure of the previous data recorded already on the disc.
However, in such the digital audio disc recording and/or reproducing apparatus, the frequencies of the recording currents are included in the AM radio broadcast band. And predetermined processes of the data signal are executed in accordance with clock pulses of various high frequencies.
Therefore the high-frequency recording current, the clock pulses and unrequited high-frequency components such as higher and lower harmonics thereof radiated from the disc recording and/or reproducing apparatus are compounded with one another and act as high-frequency noise on a radio receiver disposed in the proximity. Consequently, there occurs a problem of interference with satisfactory reception of a radio broadcast.
When merely the radio receiver alone is to be operated, the above problem is preventable by switching off the power supply of the digital audio disc recording and/or reproducing apparatus which is a source of such high-frequency noise, or by stopping the oscillation of clock pulses.
However, when a radio broadcast is to be recorded on the digital audio disc, the recording and/or reproducing apparatus is naturally not permitted to be switched off. It is therefore impossible to accomplish a satisfactory broadcast recording operation unless the above problem is valved.
A similar problem arises also in a composite audio apparatus consisting of a combination of a digital audio tape recorder or a digital compact cassette recorder and a radio receiver, or in a composite audio-visual apparatus consisting of a combination of a disc recorder/player or the like and a television receiver with a liquid crystal display.
Of the conventional methods known heretofore for eliminating or suppressing such high-frequency noise, an exemplary one is based on the use of a shield case or a filter circuit as disclosed in U.S. Pat. No. 5,165,055.